Triangular grid fill
Create a edgeloop on the other side

Starting from a similar situation



Just model the last face picking the last three vertices and press F.

Then subdivide the internal edge a with the same nuber of cuts of the vertices on the opposite side.



Now you can run the Grid Fill command



Note: the accuracy of the interpolation on the triangular tip depends on the size of the face, but nothing prevents you to subdivide the edges and make a tiny temporary face that at the end will be collapsed in one point.